Steel cord comprising preformed filaments are known in the art. The 4+6 structure of the steel cord is also disclosed.
EP0301776A1 provides a cord structure of 4+6. It discloses a low profile radial tire reinforced with steel cords composed of two layers of a core and an outer layer, the core comprising 3 or 4 filaments and the outer layer comprising a number of filaments equal to or less than the number of the core filaments, the filaments being substantially equal in diameter, the core filaments and the outer filaments having a twist of the same hand but a different pitch, the aspect ratio of the tire being at most 0.85. The patent document also discloses the cord structure can be 4+6. However the steel cord according to the patent document has no full rubber penetration. As a consequence humidity may reach the individual steel filaments during use, which may drastically decrease the life time of the steel cord and of the reinforced tire.
Full rubber penetration means that rubber must be able to penetrate into the cord between the composing elements and fill all possible interstices in order to reduce fretting and tensions between the elements and to avoid moisture from traveling along the cord, which would cause a lot of corrosion and which would considerably reduce the life of the cord and the rubber product.
WO02/088459A1 provides a steel cord comprising a first group and a second group. The first group comprises 4 filaments and the second group comprises 6 filaments. The first group is helically twisted around the second group. The first filaments have a twisting step greater than 300 mm. The second filaments are polygonally preformed. The first steel filaments have a spatial wave form. It discloses the spatial wave is not a planar wave, and it has a first crimp and a second crimp. The first crimp lies in a plane which is substantially different from the plane of the second crimp. Due to process of spatial wave, e.g. two subsequent crimps in different planes, high tensions are introduced in the first filaments and the residual stress of the first filaments is very high. It causes high sequential breaking rate of the cord. According to this the breaking load of the cord can not up to requirement. Also due to the process of spatial wave, the wear of the crimp device is high.